casual有不同含义，其含义不同，反义词也不同，具体如下：
1. relaxed and unconcerned
"a casual remark"
反义词：
premeditated
3.done or acting in a desultory way
反义词：
careful · concerned
5.not regular or permanent.
反义词：
permanent · full-time
6.employed or established on a temporary or irregular basis
反义词：
planned · intentional
8. without formality of style or manner, in particular (of clothing) suitable for everyday wear rather than formal occasions
反义词：
formal · smart
